Trilaurylamine extraction of plutonium with precipitation in oxalic acid



Nov- 4. 969 A. BATHELLIER 3,475,787

TRILAURYLAMINE EXTRACTION OF PLUTONIUM WITH PRECIPITATION IN OXALJICACID Filed Aug. 18, 1965 5 Sheets-Sheet 1 FIG/1 INVENTOR 'qNDPE BHTHELL/E/2 BY K m ATTORNEYS Nov. 4. 1969 A. BATHELLIER 3,476,787

TRILAURYLAMINE EXTRACTION OF PLUTONIUM WITH PRECIPITATION IN OXALIC ACIDFiled Aug. 18, 1965 5 Sheets-Sheet 2 Kd Pu z T I0 I I 64 f 4 W03 20 4080 I00 I00 80 60 40 2o INQENTOR I 1 ANDRE 5/2 THEL L use ATTORNEYS 7Nov. 4. 1969 A. BATHELLIER 3,476,787

TRILAURYLAMINE EXTRACTION OF PLUTONIUM 7 WITH PRECIPITATION IN OXALICACID Filed Aug. 18. 1965 5 Sheets-Sheet 3 K41 FIG.3 Pu" I I T I I 5 (#0,If I 1 I NVENTOR fl/voe 5A THELL use ATTORNEYS.

Nov. 4, 1969 A. BATHELLIER TRILAURYLAMINE EXTRACTION OF PLUTONIUM WITHPRECIPITATION IN OXALIC ACID 5 Sheets-Sheet 4 Filed Aug. 18, 1965 l .\'VE NTOR flA/op BATHELL/EE ATTORNEYS Nov. 4, 1969 A. BATHELLIER ,476i

TRILAURYLAMINE EXTRACTION OF PLUTONIUM WITH PRECIPITATION IN OXALIC ACIDFiled Aug. 18, 1965 5 Sheets-Sheet 5 FIG. 5 Hu llllllll I2345678-.9/0///2 Z.\ EX TC fin/02a BA THELL 15E BY naw/3% ATTORNEYS UnitedStates Patent 3,476,787 TRILAURYLAMINE EXTRACTION OF PLUTONI- UM WITHPRECIPITATION IN OXALIC ACID Andr Bathellier, Sceaux, France, assignorto Commissariat a IEnergie Atomique, Paris, France Filed Aug. 18, 1965,Ser. No. 480,732 Claims priority, applic9ation9France, Aug. 25, 1964,

Int. Cl. C07f /00; C22b 61/04; B01d 11/00 U.S. Cl. 260429.1 2 ClaimsABSTRACT OF THE DISCLOSURE The last stages of purification of plutoniumby solvent extraction usually consist in passing the plutonium containedin an organic phase such as trilaurylamine into an aqueous acid phasesuch as a sulphuric or sulpho-nitric acid solution and in precipitatingthe plutonium by addition of oxalic acid. However, precipitation is notcomplete and plutonium in not negligible quantities still remains insolution in the mother-liquors.

The recovery of plutonium contained in the motherliquors presents adifiicult problem. The presence in the mother-liquor both of sulphuricacid on the one hand and of oxalic acid on the other hand makes itdifficult to recover plutonium by extraction. In fact, it is known thatthe sulphuric and oxalic ions form with plutonium unextractablecomplexes. It is therefore necessary to eliminate or at least tominimize their influence. With this object in mind, a number ofsolutions have been put forward:

To increase the acidity to 8 N by addition of highly concentrated nitricacid,

To destroy the oxalic acid by nitric-acid oxidation and concentration ofthe mother-liquors.

The first solution has the disadvantage of introducing substantialquantities of nitric acid and the second solution has a disadvantage inthat it requires an evaporator which is consequently subject to rapidcorrosion by the sulphuric acid which is present, thereby entailing theneed for periodical replacement.

This invention is directed to a method for reprocessing themother-liquors derived from the oxalic-acid precipitation of plutoniumwhich overcomes the disadvantages referred-to above. Said mother-liquorsare obtained after re-extraction of plutonium from an organic phaseconsisting of trilaurylamine which may be diluted in a solvent by asulphuric acid solution and precipitation of the plutonium by additionof oxalic acid.

The method according to the invention consists in recycling themother-liquors derived from the oxalic-acid precipitation of plutoniumdirectly at the level of the trilaurylamine extraction without anyprevious treatment.

The inventor has found that, when the mother-liquors obtained from theprecipitation of plutonium by oxalic acid are recycled at the level ofthe purification by trilaurylamine extraction, there could result asufiicient dilution to ensure that the unfavorable action of thesulphate and oxalate ions is considerably reduced. Theplutonium-containing solutions which are subjected to purification bytrilaurylamine are derived, for example, from the dissolution of nuclearfuels or plutonium slags Patented Nov. 4, 1969 Ice obtained at the timeof reduction of plutonium fluoride by an alkaline-earth metal anddissolved in nitric acid.

If V V and V designate respectively the volumes of solution containingplutonium prior to extraction, after re-extraction and afterprecipitation of the oxalate (volume of mother-liquors), then there isin all cases V V but the ratio V /V which is variable according to theoperating conditions always remains distinctly higher than 5:1.Consequently, if V is recycled in V there is obtained a volume V' V +Vin which the sulphuric acid concentration and oxalic acid concentrationhave been divided by at least *6. Such solutions can be extracteddirectly with trilaurylamine.

While the experimental curve shown in FIG. 1 shows that the partitioncoeflicient between trilaurylamine dilutedto 20% in dodecane and a 2 Nnitric acid solution still, remains sufiicient in the case of lowconcentrations of oxalic acid (0.05 N) in the nitric acid phase, it wasnevertheless by no means certain that the combined action of C 05 and S0anions would not appreciably modify the partition coeflicients. Thefollowing example will in fact show that the mother-liquors can bedirectly recycled at the level of purification by trilaurylamineextraction without thereby impairing the extraction capacity of theorganic phase to any substantial extent. FIG. 2 is an analysis of thevariations in partition coefiicients of plutonium 4-]- betweentrilaurylamine diluted to 20% in dodecane and sulpho-nitric acidsolutions of variable composition. Curves 1, 2, 3 and 4 correspondrespectively to total acidities of 0.5 N, 1 N, 1.5 N and 2 N.

It can 'be seen from these curves that, in the case of a total acidityin the range of 0.5 N to 2 N, the partition coeflicients can beconsidered as acceptable if the sulphuric acidity does not exceed 20% ofthe total acidity.

In accordance with a characteristic arrangement of the invention, if theoxalic acid content in the mother-liquors were to exceed a concentrationof 0.12 Mwhich can arise only accidentallythe oxalic acid concentrationin these mother-liquors being as a rule in the vicinity of 0.04 M,ferric nitrate is accordingly added to said motherliquors in order toforestall any danger of precipitating plutonium oxalate at the time ofrecycling.

It is of interest to note that the addition of ferric nitrate offersanother advantage in that it increases the distribution coefiicient ofplutonium and facilitates its extraction as shown by the curves of FIG.3. Curves I, II and III of this figure represent the variations of thepartition coeflicients of plutonium (44+) between an organic phaseconsisting of trilaurylamine diluted to 20% in dodecane andsulpho-nitric acid solutions which have oxalic acid concentrationsrespectively of 0.5 N, 0.1 N and 0.05 N. It can be seen in particularthat the partition coefficients in the case of a plutonium-containingsolution having a 0.1 N oxalic acid concentration must be multipled by afactor of 2.5 when the ferric nitrate concentration increases from 1 to1.5 N.

There will now be given solely by way of explanatory illustration oneexample of application of the method for reprocessing mother-liquors ofoxalic-acid precepitation of plutonium in accordance with thisinvention. The practical arrangements which will be described inconnection with this example must be considered as forming part of theinvention, it being understood that any equivalent arrangements canequally well be adopted without thereby departing from the scope of theinvention.

HNO 2.5 N; H 0.15 M; H C O 0.008 M, corresponding to a mother-liquor ofoxalic precipitation of plutonium which is recycled at the level of thepurification by trilaurylamine extraction.

This solution was delivered at a rate of 16.5 volumes per hour into abank of mixer-settlers comprising 3 washing stages and 9 extractionstages having a total volume level of the purification by trilaurylamineextraction; an economy is thus achieved by dispensing with the need foran evaporator and the resulting periodical replacement of this latter.

What I claim is:

5 of 1 liter. The solution was extracted by 10 volumes per 1. Method forreprocessing mother-liquors obtained hour of trilaurylamine diluted to20% in dodecane. The after re-extraction of plutonium by a sulphuricacid solusolvent washing was carried out by 7 volumes per hour tion froman organic phase consisting of trilaurylamine of 0.5 N HNO diluted in asolvent, by oxalic acid precipitation of the After dynamic and chemicalbalancing of the mixer- 10 plutonium contained in said solution,characterized in that settler bank, and profile of concentrations ofplutonium said mother-liquors are recycled directly at the level of theand of free acidity in the different stages of the bank applutoniumpurification by trilaurylamine extraction withpeared as follows: outprevious evaporation.

Plutonium mgJl. P N tree acidity N0. of m partitioii Aqueous stageSolvent solvent coetfieient Solvent solvent 1 2 0.4 5 0.090 2 4s 2 a 0.47 7 0.143 2 20 3 3.7 0. 64 5 6 0.144 2 4 20 1 20 0.145 2 0s Extraction 527 1.6 17 0.140 2 70 6 74 0.146 2 05 7 200 20 13 0.146 2 50 8 1,000 541s 5 0.143 2 74 9 2,100 230 9 3 0.100 3 0e 10 1,800 32 50 0. 065 1 0eWashing of loaded solvent 11 1,800 32 56 0.040 0 66 12 1,800 00 0.027 05 Curves I and II of FIG. 4 represent respectively the 2. Method inaccordance with claim 1, characterized profile of plutoniumconcentrations in the aqueous phase in that ferric nitrate is added tothe mother-liquors when and in the organic phase, curves III and IV ofFIG. 5 the oxalic acid concentration in said mother-liquors is representthe profile of free acidity concentrations in these higher than 0.12 M.same phases.

It is apparent from these results that: References Cited The loss ofplutonium at the end of the extraction UNITED STATES PATENTS process isless than 510- The acidity of the loaded solvent delivered from the izggextraction process is low (0.027 N) and compatible with 2902454 9/1959Mo 00 23 312 a good re-extraction of plutonium, 2905525 9/1959 D ore 23312 While the distribution coefficients of plutonium, which 30473607/1962 fi z 12 increase from 5 to 18 in the extraction process and from3147292 9/1964 i r 23 312 56 to 90 in the washing process, are lower (byapproxi- 3154377 10/1964 ano 23*312 mately a factor of 2) than thecoefiicients obtained in the esne method of concentration of themother-liquors, they are NORMA YUDKOFF, Primary Examiner nonethelessWholly sufficient to ensure good operatlon of the extraction process. V.W. PRETKA, Assistant Examiner This example shows that the mother-liquorsderived from the precipitation of plutonium by oxalic acid can 60 berecycled directly without previous evaporation at the

